Dwarf stars likely home to nearby habitable planets

Feb. 6, 2013
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The artist's conception shows a hypothetical planet with two moons orbiting in the habitable zone of a red dwarf star. Using publicly available data from NASA's Kepler space telescope, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) estimate that six percent of red dwarf stars have an Earth-sized planet in the "habitable zone," the range of distances from a star where the surface temperature of an orbiting planet might be suitable for liquid water.
The majority of the sun's closest stellar neighbors are red dwarfs. Researchers now believe that an Earth-size planet with a moderate temperature may be just 13 light-years away.
Astronomers don't know if life could exist on a planet orbiting a red dwarf. However, this finding suggests that the most common type of the star in the galaxy may provide many more cosmic neighborhoods to search for planets that may be like our own. / D. Aguilar/Harvard-Smithsonian Center for Astrophysics

by Dan Vergano
USA TODAY
@dvergano
, USA TODAY

by Dan Vergano
USA TODAY
@dvergano
, USA TODAY

Space looks a little more crowded, astronomers report. About 6% of nearby dwarf stars likely host Earth-like planets, a science team announced on Wednesday.

The astronomy team at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., says that these "red dwarf" stars, too dim to be seen by the naked eye but by far the most common kind in space, may host many habitable worlds. The finding, based on observations made by NASA's Kepler space telescope, suggests that an Earth-sized world orbiting in its star's "habitable zone" -- not to hot or too cold for oceans -- probably resides within 13 light years of Earth, or about 77 trillion miles. That's neighbors by astronomical standards.

"They're all over the place, there are a lot of red dwarf type stars with planets out there," says astronomer Courtney Dressing, who led the team. Some astronomers call red dwarfs "the vermin of the skies", she notes, because they get in the way when they are trying to study more distant galaxies. "We now have a number and we can say that Earth-sized planets occur fairly frequently around these stars at habitable distances."

The Kepler mission in the last three years has detected some 2,700 potential planets seen in a sample of roughly 145,000 nearby stars out to about 3,000 light years away from Earth.â?? Kepler detects planets by finding the rare ones whose orbital tilt allows them to be seen from Earth as they eclipse, or "transit" in front of their star. In the study, accepted for publication by the Astrophysical Journal, the researchers looked at 3,897 red dwarfs culled from this larger Kepler star sample.

The search turned up three planets that look Earth-sized and orbit their red dwarf stars at a distance warm enough to support oceans, which is seen as a necessity for supporting life as we know it.

Because red dwarfs are dimmer than our sun, their habitable zones are closer to the stars than in our solar system, meaning the newly-discovered planets enjoy "years" lasting from 19 to 56 days. Statistically speaking, their existence means similar Earth-sized worlds likely orbit red dwarf stars even closer to us, says the astronomy team.

"That sounds like a leap but statistically it is a very fair thing to say," says Kepler astronomer Natalie Batalha of NASA's Ames Research Center in Moffett Field, Calif., who was not part of the study. "This really gives us a way forward to look for Earth-sized planets and ultimately to look elsewhere for life."

Over the last decade, astronomers have pointed to a number of these red dwarf stars, less than half the size of the sun, as potential hosts for planets in 'habitable zone' orbits. But the new finds point to statistical support for their relative frequency around red dwarfs. "We thought we would have to search vast distances to find an Earth-like planet," Dressing said. "But they are probably right in our own back yard."